Ionisation energies and electron shellsEdexcel International A Level Chemistry: Subtopic test

1. 1
   A data-analysis class is studying the ionisation energies of calcium, an element in Group 2 of the Periodic Table.

   (a)

   Which equation represents the second ionisation energy of calcium?

   [1 mark]

   • ACa⁺(g) → Ca²⁺(g) + e⁻
   • BCa(g) → Ca²⁺(g) + 2e⁻
   • CCa(g) → Ca⁺(g) + e⁻
   • DCa²⁺(g) + e⁻ → Ca⁺(g)

   (b)

   Which statement about the ionisation energies of calcium is correct?

   [1 mark]

   • AThe first ionisation energy is exothermic because energy is released when an electron leaves
   • BThe second ionisation energy is less than the first because the ion is smaller
   • CAll of its ionisation energies are endothermic because energy must be supplied to overcome the attraction between the nucleus and the electron
   • DThe third ionisation energy equals the second because the number of protons is unchanged

   (c)

   Define the term first ionisation energy.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   An unidentified element X has the following successive ionisation energies, in kJ mol⁻¹: first 578, second 1817, third 2745, fourth 11 577 and fifth 14 842.

   (a)

   In which group of the Periodic Table is element X?

   [1 mark]

   • AGroup 2
   • BGroup 3
   • CGroup 4
   • DGroup 5

   (b)

   Which statement best explains the large increase between the third and fourth ionisation energies?

   [1 mark]

   • AThe ion X³⁺ has more protons than X²⁺
   • BThe fourth electron is removed from the same shell but with more shielding
   • CElectrons in X³⁺ repel each other more strongly than in X²⁺
   • DThe fourth electron is removed from an inner shell, closer to the nucleus and less shielded, so it is held much more strongly

   (c)

   Explain why the second ionisation energy of X is greater than its first ionisation energy.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   The first ionisation energies of Group 1 elements are, in kJ mol⁻¹: lithium 520, sodium 496 and potassium 419. The second ionisation energy of potassium is 3052 kJ mol⁻¹.

   (a)

   Explain why the first ionisation energy decreases from lithium to potassium.

   [3 marks]

   (b)

   Explain why the second ionisation energy of potassium is much greater than its first. Calculate the energy needed to convert 0.50 mol of gaseous potassium atoms into gaseous K²⁺ ions.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   The first ionisation energies of the Period 3 elements are, in kJ mol⁻¹: Na 496, Mg 738, Al 578, Si 789, P 1012, S 1000, Cl 1251 and Ar 1521. The successive ionisation energies of sodium are, in kJ mol⁻¹: 496, 4562, 6910, 9543, 13 354, 16 613, 20 117, 25 496, 28 932, 141 362 and 159 076.

   (a)

   Explain the general increase in the first ionisation energy across Period 3, and the lower values for aluminium than magnesium and for sulfur than phosphorus.

   [6 marks]

   (b)

   Explain how the successive ionisation energies of sodium provide evidence for its electronic structure and for its position in Group 1.

   [6 marks]

   Total for question 4: 12 marks

End of questions